Field of the Invention
The present invention relates to a process of continuous preparation for polyester, more specifically, a process of continuous production for polyester including performing a liquid-phase polymerization under the reduced pressure in the polymerization reactor with continuously supplying an esterification or trans-esterification product with a low acid value, and an apparatus of liquid-phase polymerization capable of being applied for the process.
Description of the Related Art
A general process of producing polyester includes an esterification or trans-esterification of a dicarboxylic acid and a diol compound, pre-polymerization (precondensation), polymerization and optionally solid-phase polymerization. As the esterification or trans-esterification goes on, water (byproduct of esterification) or alcohol (byproduct of trans-esterification) is produced and needs to be discharged from the reactor. The precondensation is typically performed at a pressure of 10 to 100 torr while removing water or alcohol, unreacted diol, and/or byproducts from the reactor. Subsequent polymerization is typically performed at a reduced pressure of 0 to 10 torr while removing water, alcohol, unreacted or produced diol and the like from the reactor.
KR 10-713759B discloses a process of continuously producing polytrimethylene terephthalate including at least two-step liquid-phase polymerization including a step of continuously producing a pre-condensation product having an intrinsic viscosity of 5 or higher with a first stream of gaseous byproduct from an esterification product of terephthalic acid and 1,3-propandiol, and a step of producing a liquid-phase polymerization product having an intrinsic viscosity of 0.85 dl/g or higher with a second stream of gaseous byproduct.
U.S. Pat. No. 6,277,947 discloses a process of continuous production for polytrimethylene terephthalate (PTT) including a pre-condensation step performed under a pressure between 2 and 200 mbar and a polycondensation performed under at a pressure of 0.2 to 2.5 mbar, after at least two-step esterification.
However, the processes of continuous production for polyester must include three steps of an esterification or trans-esterification, precondensation and polycondensation performed at a separately-controlled temperature and pressure conditions and require the separate equipment collecting the byproducts produced at each step, thereby increasing the equipment cost and the production cost. Accordingly, there is a need for a simplified process and a production apparatus with an easy control of the reaction conditions.